This invention relates to measuring elevator load by load cells integrated with elevator brake anti-rotation pins, brake mountings, and calipers, and measuring elevator car line load therewith.
It has been shown in U.S. Pat. No. 3,610,342 and 4,754,850 that elevator brake reaction force can be measured so as to pretorque the motor drive in a closed loop fashion so that the motor torque exactly balances the car load, and the magnitude of current that produces the balancing torque is indicative of the live load in the car (passengers), by taking out the contribution of hoist ropes, compensation ropes and chains, and traveling cable. This can then be used to govern the generation of motor commands by the motion controller, and may be used as well for an indication of numbers of passengers in a car which is useful in dispatching algorithms. However, the methods used heretofore to eliminate contributions of ropes, chains and cables are very complex, cumbersome and time consuming. It is necessary that the apparatus which measures the brake reaction torque be of sound design, of low cost, reliable, and requiring little or no maintenance. Use of the current that balances torque to determine whether or not a live load exceeds the maximum permitted load for the car, since it can be measured only with brake off, can be dangerous, and may violate some regulatory codes.
Objects of the invention include provision of improved measurement of elevator brake reaction torque, with apparatus which is reliable, inexpensive, and requiring little maintenance; determining whether the live load in the car exceeds maximum permissible load while the brake is still engaged; and providing a simple method for extracting the live load of an elevator from elevator motor shaft load measurements, for use in motion control and dispatching algorithms.
According to the present invention, elevator brake reaction torque is measured by load cells (which may be strain gauges or the like) either on antirotation pins between the brake casing and a set of brake pads, or on load mounts between the brake casing and stationary structure, such as the motor mounting structure, including the motor casing. The load cells may measure flexure or may measure tension and compression.
In one disclosed embodiment, antirotation pins are mounted within the electromagnetic brake release coil in a manner to allow minimal flexure as the pins are distorted by brake reaction force imposed on disk brake pads tangentially to motor rotation. In another disclosed embodiment, the brake housing is mounted to a motor housing by means of load mounts containing load cells that are disposed tangentially of the rotation and measure brake reaction forces in either direction of rotation in response to both tension and compression. One guide rail brake embodiment mounts the brake with vertical load cells; another senses bending of the brake caliper jaw pieces.
In further accord with the present invention, in a preliminary process, the load in the elevator car when empty is determined, such as by brake reaction force, at each landing that the elevator serves, just prior to releasing the brake at a start of a run, and a corresponding empty car load signal is recorded for each of said landings. Thereafter, in normal operation, the empty car load value for the current landing is subtracted from a current load signal measured for the car just prior to releasing the brake for a run at any given landing, and the resulting difference signal may be utilized for motion control and dispatching algorithms, including determining whether the load in the car exceeds the maximum permissible load prior to brake release.
The invention may be used with disk brakes, caliper brakes, drum brakes, rail brakes, in roped systems, with motors in machine rooms, in elevator shafts, on cars or on counterweights, and in other systems using a brake to hold the car in a non-running position.